The present invention relates to implantable devices, and more particularly to tissue expanders and prostheses having markers to assist in locating the implant or selected area(s) of the implant once implanted. Although the tissue expanders may be used in other areas of the body, one specific application is mammary implants such as soft tissue expanders.
Tissue expanders are devices that are implanted beneath the skin or muscle and then gradually inflated to stretch the overlying tissue. Expanders are commonly used either to create a pocket for receiving a permanent prosthesis, or to generate an increased skin surface area in anticipation of the new skin being utilized for grafting or reconstruction.
Conventional implantable mammary tissue expanders are formed of a silicone polymer shell. After implantation, a fluid, such as saline, is periodically injected into the expander to enlarge it over time. Between injections, the surrounding skin is permitted to stretch and grow to create the increased skin surface and the increased tissue pocket for receipt of the permanent implant. Typically, a tissue expander will be provided with an injection element through which fluid can be introduced into or withdrawn from the expander. One such injection element is an integrated injection dome comprising a septum that can be pierced with a hypodermic needle for the introduction into or withdrawal of fluid from the expander. Alternatively, the injection element may be a self-sealing area on the tissue expander which allows penetration by a hypodermic needle and self-closing after the withdrawal of the needle.
It can be difficult, however, to accurately locate the injection element through the overlying tissue once the expander has been implanted. If the injection element is missed and the needle punctures the shell of the tissue expander, the expander can leak, which typically requires removal and replacement of the expander. In an effort to reduce the likelihood of inadvertent puncture, one known device provides an injection element surrounded by a self-sealing member, which provides a safety zone around the injection element. This type of arrangement is disclosed, for example, in the U.S. Pat. No. 6,743,254, the disclosure of which is hereby incorporated by reference herein. Other solutions include providing a palpation ring around the injection element. It still can be difficult, however, to identify the proper location through tissue, and a raised palpation ring may cause additional pain and discomfort to the patient. Other known expanders use a magnetic component near or around the injection dome (such as sealing ring) or behind the dome (such as a needle stop). A detection device is then utilized to locate the magnetic component through interaction with the magnetic field. Yet other known devices have used radiographic detection of the access port, such as is disclosed in U.S. Pat. Nos. 8,382,723 and 8,382,724 and U.S. Patent Publication Nos. 2006/0264898 and 2010/0198057.
U.S. Patent Publication No. 2011/0275930, entitled “SYSTEMS AND METHODS FOR IDENTIFYING AND LOCATING AN IMPLANTED DEVICE”, discloses a system for identifying an attribute of an implanted medical device, such as an access port. In one embodiment, the identification system includes a marker and an external detection device with a signal source that emits an incident electromagnetic signal for impingement on the marker and a detector that detects a return signal from the marker, and a user interface for conveying information relating to the attribute based on detection of the return signal. In the case of an implantable access port, for instance, the described system enables information, such as the ability of the port to withstand power injection of fluids therethrough, to be ascertained even after the port has been subcutaneously implanted within the patient.
Systems and methods of the types described above are not ideal. Magnetic field based detection systems incorporate magnets or metallic parts, which may be undesirable to some patients, and which result in difficulties in passing through airport security or undergoing MRI procedures, etc. Radiographic detection systems require additional exposure to radiation, which is undesirable. Further, these types of devices require additional parts, which add to the cost of the expander itself. Thus, there is a need to provide an implant including an improved marker for more readily locating the implant once implanted.